As described in US Patent Application Publication No. 2011/0221161 by Ludovici et al, a typical wheelchair includes a seat supported by a frame resting upon four wheels. A front wheel and a rear wheel are disposed on each side of the wheelchair. The pair of rear wheels may be located under or behind a seat upon which the occupant of the wheelchair is seated. The front wheels are located in front of the rear wheels and pivot to facilitate steering. Generally, the rear wheels are mounted to opposite sides of the frame by an axle assembly. Generally, the front wheels are mounted to opposite sides of the frame by a bearing fork assembly.
In many wheelchair designs, the front wheels have a significantly smaller radius than the rear wheels. Therefore, the axles of the rear wheels are typically mounted to the frame at locations that are elevated from the locations of attachment of the axles of the front wheels to the frame. In this manner, an angle of the frame relative to the ground may be determined by the locations in which the front and rear wheels are mounted to the frame and the diameter of the front and rear wheels, or by the manufacturer of the custom wheelchair frame.
An angle is defined between the frame and the ground. For front and rear wheels each having a predetermined and substantially constant diameter, the angle may be determined by the attachment location of the front wheels relative to the attachment location of the rear wheels. Because it may be desirable to adjust the seat angle relative to the ground in some wheelchair designs, the vertical and/or horizontal positions of the rear and/or front wheels relative to the frame may be adjusted.
Each of the front wheels is mounted to the longitudinal frame member by a bearing fork assembly. In many wheelchair designs, the bearing fork assembly includes a bearing fork and an upright pivot pin, which may be implemented as a stem bolt. The bearing fork is coupled to an axle about which the front wheel rotates. The upright pivot pin pivotally couples the bearing fork to the frame. To steer the wheelchair, the bearing fork pivots about the upright pivot pin.
As a general rule, it is desirable to orient the upright pivot pin generally perpendicular to the ground. If the upright pivot pin is not perpendicular to the ground, the front wheels may not pivot properly. Further, because the front wheels typically pivot to facilitate steering the wheelchair, if the upright pivot pin is not perpendicular to the ground, the front wheel may not rotate properly and the steering of the wheelchair may be impaired.
A wheelchair may require adjustment to fit a particular user. For example, many wheelchairs allow the user to adjust the height of the seat by vertically moving the location where the frame attaches to the rear axles. This adjustment will typically modify the angle of the seat relative to the ground. Similarly, some wheelchair designs allow a user to move the rear wheels longitudinally forward and backward relative to the seat, which may also modify the angle of the seat.
The ability to change the angle of the seat is important to proper positioning of the wheelchair occupant. Increasing the angle of the seat (i.e., increasing the height of the front of the seat relative to the back of the seat) allows gravity to help prevent the occupant of the wheelchair, who will likely have limited or no lower extremity function and perhaps limited trunk muscular control, from sliding out of the seat.
Often, finding the correct angle of the seat is a matter of trial and error. Over time, the most desirable angle may change. For example, a particular wheelchair user may have a degenerative disease that requires increasing the angle over time. Alternatively, as people age they become more susceptible to pressure sores. By reducing the angle of the seat, it is possible to reduce the pressure on the buttocks.
If the angle of the frame relative to the ground is changed, the angle of the upright pivot pins of the bearing fork assemblies may require adjustment to reorient the upright pivot pins perpendicular to the ground. Therefore, a need exists for devices that rotate the upright pivot pins to which the bearing forks are mounted to position the upright pivot pins perpendicular to the ground.
Although various devices exist in the prior art which provide some angular adjustment of the upright pivot pins, most prior art configuration either: i) are limited to a few preselected orientations; ii) are limited in overall range of adjustment permitted; iii) require considerable disassembly and reassembly to adjust; or iv) a combination of the above.